In motor vehicles there is a need to force air flow through the radiator in order to obtain more rapid dissipation of heat from the cooling liquid to the exterior. The forced air flow is obtained by causing the rotation of an apparatus which is normally mounted either directly on the drive shaft of on the shaft of the water pump or on a driven shaft carrying a pulley which is connected by a belt to the drive shaft.
An apparatus which allows continuous adjustment of the quantity of air forced onto the heat exchanger which cools the fluid is also known. This apparatus has a central body mounted on a rotating support and a plurality of blades radially mounted by means of associated coupling devices on said central body, said blades being rotatable about their respective longitudinal axes upon operation of movement actuating and transmission means forming part of the apparatus.
An example of such an apparatus is that for example described in EP 0,967,104.
Such apparatus can have the drawback that the blade-support assembly continues to rotate even when the angle of incidence of the blades is at a minimum, thus resulting in an undesirable drawing of power with an associated increase in the fuel consumption and constant noisiness, even when the climatic and operating conditions are such that the cooling fan need not be used.